We are very pleased with the Kenda Kwest K193 37-622 tires on our T50. The fastest we have riden it is 25 mph; typically we cruise in the 12 to 15 mph range. We run the tires at 95 to 100 psi - though they are rated at 85 psi max. We use Avenir Thorn resistant tubes (700 - 35/45) and Stop Flats 2 Gold liners - never had a flat. Did have a tube come apart at the stem when trying to get the valve chuck off after inflating it.

Unless you are going for sustained speeds over 20 mph, a narrow tires will not increase your speed.

A lighter tire will allow you to accelerate faster due to lower rotational inertia.